/*
 * Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package javax.xml.xpath;

import javax.xml.namespace.QName;

/**
 * <p><code>XPathVariableResolver</code> provides access to the set of user defined XPath
 * variables.</p>
 *
 * <p>The <code>XPathVariableResolver</code> and the XPath evaluator must adhere to a contract that
 * cannot be directly enforced by the API.  Although variables may be mutable, that is, an
 * application may wish to evaluate the same XPath expression more than once with different variable
 * values, in the course of evaluating any single XPath expression, a variable's value
 * <strong><em>must</em></strong> not change.</p>
 *
 * @author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @since 1.5
 */
public interface XPathVariableResolver {

  /**
   * <p>Find a variable in the set of available variables.</p>
   *
   * <p>If <code>variableName</code> is <code>null</code>, then a <code>NullPointerException</code>
   * is thrown.</p>
   *
   * @param variableName The <code>QName</code> of the variable name.
   * @return The variables value, or <code>null</code> if no variable named
   * <code>variableName</code> exists.  The value returned must be of a type appropriate for the
   * underlying object model.
   * @throws NullPointerException If <code>variableName</code> is <code>null</code>.
   */
  public Object resolveVariable(QName variableName);
}
